In this experimental study, the effect of zeolite on the properties of autoclaved aerated concrete (AAC) was investigated. Zeolite was used as a quartzite replacement in conventional AAC mixtures. The zeolite containing AAC (ZAAC) specimens were prepared at bulk densities of 270-500 kg/m (3). The specimens were examined by X-ray diffraction, X-ray fluorescence, and thermal analysis. Bulk density, compressive strength and thermal conductivity parameters were investigated. According to the results of research, the commercial AAC is mainly composed of tobermorite, quartz and anhydrite, but the specimens of ZAAC, besides tobermorite and quartz, contain unreacted anhydrite and clinoptilolite phases. XRD patterns of ZAAC obtained after treatment at 700-1000 degrees C show that wollastonite, gehlenite and orthoclase are the new phases formed. It was observed that application of zeolite in AAC significantly lowered the thermal conductivity of autoclaved products (0.08-012 kcal/mh degrees C) providing the compressive strength at the level of 1.22-3.34N/mm(2). (c) 2006 Elsevier Ltd. All rights reserved.